This invention relates, generally, to a surface mounting device and more particularly to a device and method for compliant interconnection between a substrate and a surface mounting device through the use of an interposer.
As a result of lowering assembly cost, surface mounting devices are being utilized more and more frequently. However, if a ceramic chip carrier or the like is directly soldered to a printed circuit board, problems may occur due to the large coefficient of expansion mismatching between the ceramic and the printed circuit board. Additionally, due to the nonsymmetrical structure of printed circuit boards, they have a tendency to undergo a deformation with the result that "potato-chipping" occurs with the curvature of the printed circuit board changing with temperature and time. When solder is utilized to attach the chip carrier or the like to the printed circuit board, columns of solder couple the two components together. These columns are short and therefore elongation or elastic properties of the columns are poor, with the result that the interface is readily susceptible to cracking. Two types of devices which may utilize surface mounting in conjunction with solder may be found in U.S. Pat. No. 4,268,102 "Low Impedance Electrical Connecting Means for Spaced-Apart Conductors" issued May 19, 1981 to Grabbe, and U.S. Pat. No. 4,155,615 "Multi-Contact Connector for Ceramic Substrate Packages and the Like" issued May 22, 1979 to Zimmerman, Jr., et al.
Accordingly, it is desirable to create a higher solder pedestal so that substantial compliance will be available to compensate for thermal coefficient of expansion mismatch or "potato-chipping". It is also desirable to have this pedestal utilized as an interposer, that is between a substrate and a component, being relatively inexpensive to utilize as well as manufacture and not requiring significant additional or different steps than previous methods. Such a device is taught in the present invention.
Accordingly, and as a further object of the present invention there is described a device for compliantly attaching a connector to a substrate, comprising a substrate having at least one conductive strip thereon, an electrical connector housing disposed on the substrate and having at least one electrical contact disposed therein, wherein the electrical contact has a pad in opposing relationship to the conductive strip and an interposer is disposed between the substrate and the electrical connector housing, with the interposer being comprised of a nonconductive carrier having at least one interconnect area disposed therein and an interconnect area is disposed between a conductive pad and a corresponding conductive strip, and further characterized by at least one wire having solder or the like thereon such that upon soldering, the solder and wire form a compliant electrical interconnection between a conductive pad and a corresponding strip. Another object of the present invention is for a method for compliantly interconnecting an electrical component or connector to the substrate, comprising the steps of: (a) placing the interposer onto the substrate such that the interconnect areas are in alignment with corresponding conductive strips on the substrate; (b) placing the electrical connector adjacent the interposer such that portions of the electrical contacts in the connector are in alignment with a corresponding interconnect area in the interposer; and (c) heating the interconnect areas so as to form a soldered connection between the conductive pads and the corresponding conductive strips.